1. Field of the Invention
This invention relates to a traffic shaping apparatus for an ATM (Asynchronous Transfer Mode) network, and more particularly to a dynamic shaping apparatus which sends out cells into a virtual path or a virtual channel set on an ATM transmission line in an ABR service by an ATM network varying the sending out distance between the cells.
2. Description of the Related Art
In recent years, an available bit rate (ABR) service has been recommended as a service by an asynchronous transfer mode (ATM) network, for example, in the ATM Forum Traffic Management Specification, Version 4.0, April 1996, which will be hereinafter referred to simply as ATM Forum TM. 4.0.
The ABR service is a kind of service which does not compensate for the transmission quality of cell delaying but compensates for the quality of cell losing. In the ABR service, an allowable cell rate (ACR) which is a sending cell rate of a terminal is dynamically allocated in response to a congestion condition of the network. It is to be noted that the "terminal" used in the present specification may be a real terminal actually used by a user which may be called an "end-system (ES)" on a Virtual Source/Virtual Destination (VS/VD) defined in the ABR service, for example, in the ATM Forum TM 4.0.
Where the ABR service is applied to a public network, similarly to a constant bit rate (CBR) service or a variable bit rate (VBR) service provided conventionally, a usage parameter control (UPC) must be installed in a user network interface (UNI). The usage parameter control is used to check the cell conformance that the user sends as traffic and observes a cell rate contracted by the user. Further, a network parameter control (NPC) must be installed in a network node interface (NNI).
However, since the UPC and the NPC used in the conventional CBR and VBR services do not presuppose that a terminal dynamically varies the cell rate in response to a congestion condition of the network, they cannot perform policing conforming to a dynamic variation of the cell rate at which traffic is sent out from the terminal.
Therefore, a UPC and an NPC for the ABR service are provided, and a DGCRA (Dynamic Generic Rate Algorithm) is proposed as an algorithm for the UPC and the NPC, for example, in the ATM Forum TM 4.0.
FIG. 12 is a diagrammatic view of a conventional ATM network which provides the ABR service.
Referring to FIG. 12, a transmission terminal (as a Source End-System (SES) in the ATM Forum TM 4.0) 102 and a reception terminal (as a Destination End-System (DES) in the ATM Forum TM 4.0) 103 are connected to an ATM network 101, and a UPC 104 is provided for a UNI 105 located at an entrance of the ATM network 101.
When the transmission terminal 102 tries to send data to the reception terminal 103, it sends a forward resource management cell (FRM cell). When the FRM cell is received by the reception terminal 103, the reception terminal 103 sends back the FRM cell as a backward resource management cell (BRM cell) to the transmission terminal 102.
When the FRM cell from the transmission terminal 102 or the BRM cell from the reception terminal 103 passes the ATM network 101, the ATM network 101 writes a current congestion condition thereof into the FRM cell from the transmission terminal 102 or the BRM cell from the reception terminal 103.
The transmission terminal 102 varies the sending rate in response to an explicit rate (ER) written in the BRM cell from the reception terminal 103.
The UPC 104 performs policing in response to the DGCRA mentioned above. In the DGCRA, the UPC and the NPC monitor the ER written in the BRM cell from the reception terminal 103, and predicts a rate variation of the terminal based on the ER and then effects policing based on the predicted rate variation.
However, since a UPC and an NPC are usually installed at a location spaced by a large distance from a terminal, a propagation delay is produced when a cell moves between the terminal and the UPC and NPC. Accordingly, a time difference is produced between rate variation operations of the UPC and NPC and the terminal by the propagation delay.
Further, as described above, the ABR service guarantees loss of a cell, but does not guarantee a delay of a cell. On the other hand, a delay of a cell is guaranteed in the CBR service and the VBR service.
Consequently, in an ATM network which provides plural services, a cell of the ABR service is lower in priority in cell sending out than a cell of the CBR service or the VBR service at a terminal and an exchange.
Accordingly, in the ABR service, the cell delay variation (CDV) in the network is increased by priority control by an exchange interposed between the terminal and the UPC and NPC, and the arrival time of the cell at the terminal varies by a large amount. Consequently, the arrival of the BRM cell to the transmission terminal varies by a large amount, and the timing of updating of the sending rate in the transmission terminal varies by a large amount. Consequently, the UPC and NPC exhibit a large variation in time with respect to the variation point of the rate.
Referring to FIG. 12, reference symbol t2 denotes a time required until the UPC 104 varies the monitoring rate after the UPC 104 predicts that the rate of the transmission terminal 102 will vary. This time t2 varies between .tau.3 which is a minimum time and .tau.2 which is a maximum time.
Against the problem described above, the DGCRA increases, when the rate of the transmission terminal 102 increases, the monitoring rate after lapse of .tau.3 which is the shortest time within a prescribed range after the UPC 104 predicts that the rate of the transmission terminal 102 will vary, but decreases, when the rate of the transmission terminal 102 decreases, the monitoring rate after lapse of .tau.2 which is the longest time within the prescribed range. Accordingly, the DGCRA has a margin of .tau.2-.tau.3 to a time until the monitoring rate is varied after the UPC and NPC predicts that the rate of the transmission terminal will vary.
However, when the CDV in the network is large, the timing of updating of the transmission rate in the transmission terminal varies by a large amount. Accordingly, since the variation point of the rate varies by a large amount in time, the UPC and NPC must take a large margin in conformity with the time variation. Since an increase of the margin increases the band allocation to a user, there is a problem in that the utilization efficiency of the network is degraded.
Further, similar to the CBR service and the VBR service, the ABR service is required to produce traffic in which the cell delay variation (CDV) is reduced in advance to simplify designing the capacity of a network.
Meanwhile, from the situations of the user and the opposing network sides, production of cell traffic which is not determined to be non-conforming by the UPC and NPC of the destination of the connection is required.
In order to solve the problems described above, similar to the CBR service and the VBR service, the ABR service requires a traffic shaping apparatus which is an apparatus for shaping traffic.
Conventionally, traffic shaping apparatus have been proposed for the CBR service and the VBR service. One such traffic shaping apparatus is disclosed, for example, in Japanese Patent Laid-Open Application No. Heisei 4-100451.
Further, an example of an arrangement of a conventional traffic shaping apparatus for the CBR service and the VBR service has been proposed, and also it has been proposed to install a traffic shaping apparatus, not only in the UNI or the NNI at an entrance of an ATM network, but also in an exchange in the network, for example, in Japanese Patent Laid-Open Application No. Heisei 4-100342.
However, in such a conventional traffic shaping apparatus for the CBR service or the VBR service as described above, the rate (shaping cell rate) for sending of cells of the traffic shaping apparatus is determined based on a set peak cell rate (PCR) and a sustainable cell rate (SCR). Consequently, the shaping cell rate is fixed within a call setting period. Accordingly, the conventional traffic shaping apparatus Is disadvantageous in that, when the sending cell rate of a terminal varies, it cannot respond well to the rate variation.
Further, since the conventional traffic shaping apparatus for the CBR service or the VBR service does not have a function of acquiring from the network, information of sending cell rates of a terminal at the present and in the future, it Is disadvantageous in that it cannot detect a rate variation of a terminal. Consequently, the conventional traffic shaping apparatus for the CBR service or the VBR service cannot predict a rate variation of a terminal. As a result, the traffic shaping apparatus for the CBR service or the VBR service is disadvantageous also in that it cannot be used as it is for the ABR service.
Further, conventionally proposed apparatus which provide ABR service traffic do not involve traffic shaping in a network. For example, as an ATM communication apparatus which can provide ABR service traffic, a terminal and an exchange which can handle traffic of the ABR service are disclosed, for example, in Japanese Patent Laid-Open Application No. HEISEI 7-297843.
However, policing and traffic shaping for the ABR service have not been proposed as yet.
Accordingly, the ATM communication apparatus which can provide ABR service traffic described above cannot solve the problems in regard to the ABR service described above since traffic cannot be shaped intermediately of the network.